A Co-ordinate Measuring Machine (CMM) Arm is an articulated measuring apparatus comprising two or more links connected by intervening joints. It serves as a movable position reporting device which monitors the internal angles adopted by said links so that the position and orientation of a probe end can be calculated with some accuracy, typically below 0.1 mm. A CMM arm usually comprises the probe end to support a measuring device such as a non-contact probe. A CMM Arm is well known in the art. It is mainly used in metrology applications. A CMM Arm is a manual apparatus; this means that a human operator must manually move and sometimes support the arm in the desired position to take measurements. Manufacturers of such arms are, for example, Faro or Cimcore.
A robot is also an apparatus that is articulated, comprising two or more links and joints and a probe end for supporting tools and/or measurement devices. It serves as a movable member. However, unlike the CMM Arm, the robot links can be moved by a powered means e.g. servo or hydraulic mechanisms. Although it possesses the capability of giving some position and orientation information about the probe end, its accuracy is not as good as that of a CMM Arm. Therefore, robots are not used for high precision metrology applications. Manufacturers of robots are, for example Kuka or Fanuc.
A Robot CMM Arm (RCA) combines the powered movement of a robot with the accuracy of CMM Arm. An RCA thus comprises a movable member i.e. a robot; a movable position reporting device i.e. CMM Arm; and a transmission means in contact with both said movable member and said movable position reporting device. The elements are configured so the movements of the robot are transmitted to the CMM Arm via the transmission means. In practice, the robot of the RCA replaces the hands of the human operator, enabling the weight of CMM Arm to be taken by the movement mechanisms, and allowing semi- or automated movement of the probe end. High precision metrology applications are, therefore, possible in an automated way with an RCA.
RCA with Manual Control
The control of an RCA is by use of buttons provided on the arm. It requires much training and skill to operate in order to guide the probe to the desired position that is close enough to take a reading without colliding with the object being scanned. It is necessary that the acceleration and speed of the robot is slow under manual control, which slows down measurements. Furthermore, system of precautionary collision sensors and buffers becomes essential which add to the expense and weight of the RCA. The present invention overcomes the problem of controlling the RCA such that more accurate measurements are taken while reducing the risk of collision.
Robust RCA with Exoskeleton
An example of an RCA includes the RCA with Exoskeleton as disclosed in PCT/GB2004/001827 by Crampton the inventor of this present invention, which application is incorporated herein by reference. A Probe End Module for Articulated Arms is disclosed by Crampton in GB0424729.2. An RCA with Exoskeleton comprises an Internal CMM Arm 5 and an Exoskeleton 6 as depicted in the Figures of PCT/GB2004/001827 (e.g. FIG. 1C). On a production line, equipment lifetime operating cycles in excess of ten million cycles are not uncommon with Mean Time Between Failures of greater than 10,000 hours being expected. Line equipment ingress protection ratings against liquids and solid bodies of IP54 or greater are often demanded. For an RCA with Exoskeleton to be robust, all mechanical, electrical and software systems must have a concept and design to achieve these requirements. Our experience in overcoming the challenges of developing an RCA with Exoskeleton for demanding environments has led to the present invention.